1. Field of the Invention
The present invention relates to a resin-packed type optical fiber unit used in the field of optical communications or the like.
2. Description of the Related Art
In the field of optical communications and the like, a resin-packed type optical fiber unit which is made by collecting a plurality of optical fiber cores and integrating them using resin. The resin-packed optical fiber unit has a structure as shown in FIG. 1. As shown in this figure, a resin-packed optical fiber unit 1 comprises a tension member 2 situated at a center of the unit, optical fiber cores 3 arranged to surround the tension member 2, an inner layer unit packing member 4 for fixing the tension member 2 and the optical fiber cores 3, and an outer layer unit packing member 5 applied on the inner layer unit packing member 4. A plurality of the optical fiber units 1 are further collected together to form, for example, an optical fiber cable running along the sea bed (an optical submarine cable).
In this optical fiber unit 1, the outer layer unit packing member 5 is made of a relatively hard resin such as an ultraviolet ray hardening resin (abbreviated as UV resin, hereinafter), and therefore the material 5 serves to protect the optical fiber core 2 from an external force. The inner layer unit packing member 4 is made of a relatively soft resin such as a UV resin, which serves to relax an external force, thus protecting the optical fiber cores 2. In general, UV resins harden quickly and entail high productivities, and therefore they can be utilized as packing members for an optical fiber unit.
The resin material of the outer layer unit packing member 5 should preferably be of a type having a high tear elongation ratio, for the purpose of preventing damages to the optical fiber unit due to the external force. Therefore, conventionally, a resin having a tear elongation ratio of as high as about 7% is used as the material for the outer layer unit packing member.
An optical fiber unit of the above-described type, when used in practice, must be processed at its end portion to peel off the covering and expose the optical fiber core, which is connected to the optical fiber core of another optical fiber unit. Therefore, it is preferable that the optical fiber core be easily separated from the optical fiber unit, more specifically, the packing members which constitute the optical fiber unit.
As can be seen in FIGS. 2A to 2C, in the process of an end portion of the optical fiber unit 1, the end portion of the optical fiber unit 1 is divided into a divisional optical fiber unit 1a which includes an optical fiber cores 3a and 3b, and a divisional fiber unit 1b which includes optical fiber cores 3c and 3d. FIG. 2A is a side view of the optical fiber unit 1 which is subjected to the process of the end portion. FIG. 2B is a cross sectional view of the divisional optical fiber unit 1a. FIG. 2C is a cross sectional view of the divisional fiber unit 1b.
As can be seen in the above figures, when the end portion of the optical fiber unit 1 is divided into two, both of the inner layer unit packing member 4 and the outer layer unit packing member 5 are not equally divided. More specifically, when the end portion of the optical fiber unit 1 is divided, cross sections of these portions will have the following shapes. When the cross section of the divisional optical fiber unit 1a is, for example, quasi-circular such as shown in FIG. 2B, the cross section of the fiber unit 1b will have a shape having a recess corresponding to the cross sectional shape of the fiber unit 1a, with nail-like end projections C. Consequently, in the case where the end portion of the optical fiber unit 1 is divided in the process and the divisional optical fiber units 1a and 1b are in a course of separating from each other, the fiber unit 1a is caught by the nail-like end projections C of the fiber unit 1b. If the fiber units 1 and 1b are forcibly separated from each other, the optical fiber cores 3a and 3b are broken. Further, the optical fiber cores 3c and 3d are in a process of separating from the optical fiber unit 1b, the optical fiber cores 3c and 3d are caught by the end projections C of the optical fiber unit 1b. If they are forcibly separated, the fiber cores 3c and 3d are broken. As described above, the conventional resin-packed optical fiber unit entails the problem in which an end portion of the unit cannot be easily processed.